1. Technical Field
This invention relates to improved metal bond abrasive tools. More particularly, the present invention relates to improved diamond abrasive cutting tools having two or more electroplated layers of diamond particles, in which each layer has diamond particles of different size, to provide the benefits of relatively good surface finish and high feed rate.
2. Background Information
Superabrasives such as diamond and cubic boron nitride (CBN) have been widely used on saws, drills, and other tools to cut, form or polish other hard materials.
Diamond tools are particularly useful in applications where other tools lack the strength and durability to be practical substitutes. For example, diamond saws are routinely used in the stone cutting industry due to their hardness and durability. If superabrasives were not used, many such industries would be economically infeasible.
Despite the improvements provided by diamond and cubic boron nitride for cutting, drilling, and grinding tools, disadvantages still exist which, if overcome, may greatly improve tool performance, and/or reduce their cost.
A typical superabrasive tool, such as a diamond saw blade, is manufactured by mixing diamond particles with a suitable matrix (bond) powder. The mixture is then compressed in a mold to form the desired shape (e.g., a saw segment). The “green” form is then consolidated by sintering at a suitable temperature to form a single body with a plurality of superabrasive particles disposed therein. Finally, the consolidated body is attached (e.g., by brazing) to a tool body, such as to the round blade of a circular saw, to form the final product.
Abrasive tools using metal bond material have been used to fabricate slicing or cut-off discs. One such tool, commonly referred to as metal matrix composite (MMC) tool, may be formed by molding a mixture of abrasive and metal bond material. An example of such a tool is disclosed in U.S. Pat. No. 5,313,742, assigned to Norton Company of Worcester, Mass. As described therein, such discs may include porosity which varies from essentially zero porosity by volume to as much as 40 or 50% porosity by volume. The preferred volume percent composition of the discs are 5 to 50% by volume of abrasive, 50 to 95% by volume of bond, and 0 to 25% by volume of pores. The bond includes any of the metal bonds well known in the industry, used primarily to bond diamond and cubic boron nitride (CBN) abrasive grits. Examples of such metal bonding material are alloys such as Cu—Zn—Ag, Co—WC, Cu—Ni—Zn, Cu—Ni—Sb, Ni—Cu—Mn—Si—Fe, Ni—Cu—Sb—TaC.
Another type of metal bonded tool is formed by electroplating, such as set forth in U.S. Pat. No. 4,381,227, also assigned to Norton Company, and also fully incorporated by reference herein. This reference discloses placing a substrate within an electroless plating bath having abrasive grain dispersed therein. A direct current is applied through the bath with the substrate as the cathode and an electrode containing the plating metal being positioned in the bath as the anode. This reference states that a current density in the case of a nickel plating electroless bath can be as low as from 1.5 to 5 amperes per square foot (1.4 to 4.6 mA/cm2), but should preferably be from 50 to 100 amperes/ft2.
The abrasive grits, which may be diamond, cubic boron nitride, silicon carbide, alumina, co-fused alumina-zirconia, or even flint, may be allowed to settle from suspension onto the substrate or may be positioned adjacent the substrate as by a carrier or basket.
Variations of the foregoing tools are often used as slicing or cut-off discs for cutting through hard materials such as hardened steel, or for cutting ceramics typically used in the electronics industry. The choice of abrasive size (grit size) generally entails a trade-off between feed rate and surface finish. For example, larger grit sizes may be used in cutting applications where high feed rate is of primary importance. The aforementioned MMC tools have generally been favored for such applications. Conversely, smaller grit sizes, often used with the aforementioned electroplated wheels, may be used in applications that require a high quality surface finish.
A need exists for an abrasive cutting tool that provides the heretofore mutually exclusive benefits of high feed rate and high quality surface finish.